Abnormal vitamin D metabolism in patients with psoriasis.

To elucidate if psoriatic skin involvement induces changes in vitamin D metabolism, the serum concentrations of the major vitamin D metabolites (25-hydroxy-vitamin D(2+3) (25OHD), 1,25-dihydroxyvitamin D(2+3) (1,25(OH)2D), and 24,25-dihydroxyvitamin D(2+3) (24,25(OH)2D)) were studied in a group of patients with psoriasis, who had not been exposed to ultraviolet radiation at least three months before the investigation. Serum concentrations of 1,25(OH)2D were significantly reduced in 17 patients with disseminated psoriasis compared to healthy age and sex matched controls (22.3 pg/ml versus 35.0 pg/ml (p less than 0.001)) and compared to 15 patients with moderate extended psoriasis (22.3 pg/ml versus 38.3 pg/ml (p less than 0.005)). Serum concentrations of the two other metabolites were not significantly decreased. In patients with moderate psoriatic skin manifestations, the values of the three vitamin D metabolites were normal. It is concluded that patients with disseminated psoriasis demonstrate decreased serum concentrations of the vitamin D metabolite 1,25(OH)2D. Since 1,25(OH)2D plays a role in differentiation and proliferation of epidermal cells, the abnormal low serum level of 1,25(OH)2D might be of importance for the abnormalities in cell maturation and proliferation found in psoriatic skin.